Retroreflective articles have the ability to return incident light--that otherwise would be reflected elsewhere--back towards the light source. This unique ability has led to widespread use of retroreflective articles on clothing. Persons who work or exercise near motor vehicle traffic need to be conspicuously visible, particularly at nighttime, so that they do not get struck by passing motor vehicles. Retroreflective articles serve the purpose of highlighting a person's presence by retroreflecting light from motor vehicle headlamps or other light sources.
A retroreflective article typically comprises a layer of optical elements, a reflective layer, and a polymeric binder layer. The optical elements usually are transparent microspheres that are partially embedded in the polymeric binder layer such that a substantial portion of each microsphere protrudes from the polymeric binder layer. The reflective layer is disposed beneath the embedded portion of the transparent microspheres. Light striking the front surface of the retroreflective articles passes through the transparent microspheres, is reflected by the reflective layer, and is collimated by the transparent microspheres to travel back in the direction of the light source. layer, and is collimated by the transparent microspheres to travel back in the direction of the light source.
Retroreflective articles that are used on clothing, particularly shoes, may be subjected to high levels of abrasion, as might be produced, for example, by bombardment of sand, gravel, or other debris, or by rubbing against concrete or other abrasive surfaces. Retroreflective articles used in such environments therefore should demonstrate good abrasion resistance.
Retroreflective articles applied onto clothing that is normally laundered must also be able to withstand laundering conditions. If the retroreflective article is not durable to laundering, and retroreflectivity becomes substantially diminished after repeated washings, the clothing cannot continue to serve its safety function by highlighting the wearer's presence. Investigators in the retroreflective art have pursued an ongoing goal of developing launderably durable retroreflective articles so that persons wearing retroreflective clothing can continue to be conspicuously visible after the clothing has been worn and cleaned many times. On the other hand, some articles of clothing, such as shoes, are not routinely laundered. For articles of this type, launderability is a less stringent requirement, and some launderability may be sacrificed in favor of increased abrasion resistance.
In a successful attempt at developing an exposed lens retroreflective article that is durable under industrial laundering conditions. Wu Shyong Li in U.S. Pat. 5,200,262 partially embedded a monolayer of metal-coated microspheres in a binder layer that contained a flexible polymer and one or more isocyanate-functional silane coupling agents. The flexible polymers include isocyanate curable polyesters and one or two component polyurethanes.
In another successful attempt, Li used a binder layer that was formed from an electron-beam curable polymer and typically one or more crosslinkers and silane coupling agents (see U.S. Pat. No. 5,283,101). The electron-beam curable polymers included chlorosulfonated polyethylenes, ethylene copolymers comprising at least about 70 weight percent of polyethylene such as ethylene/vinyl acetate, ethylene/acrylate and ethylene/acrylic acid, and poly (ethylene-co-propyulene-co-diene) polymers. The microspheres were embedded in the cured binder layer, and a specular reflective metal layer was disposed on the microsphere's embedded portions.
In another approach, Michael Crandall et al. disclosed making a retroreflective article launderably-durable by placing a compound that contains an aromatic bidentate moiety in chemical association with the reflective metal layer. In one embodiment, the compound is disposed in a polymeric binder layer that preferably includes a crosslinked or virtually crosslinked elastomer. Crosslinked polymers include polyolefins, polyesters, polyurethanes, polyepoxides, and natural or synthetic rubbers. This product is disclosed in U.S. Pat. No. 5,474,827.
In U.S. Pat. No. 5,645,938, Michael Crandall made a further contribution to the art by producing a launderably durable retroreflective article that included a binder layer that comprised a polyester polyurethane polymer. The polyurethane polymer is a reaction product of (i) a polyester polyol that contains an aromatic nucleus and that has at least two isocyanate groups bonded non-conjugatively to the aromatic nucleus, and (ii) a polyisocyanate.
Several references have discussed adhesives that are made from silicon-containing polymers and epoxy resins. European Patent Application 0 370 464 A2 to Kanegafuchi Chemical Industry discloses a curable resin composition comprising specified amounts of an organic rubbery polymer having a crosslinkable group --Si(R.sup.1)(OR.sup.2).sub.2, an epoxy resin, a silanol condensation catalyst, a curing agent, and a silicon compound such as aminopropylmethyldiethoxysilane. U.S. Pat. No. 4,562,237 to Okuno discloses a curable sealant comprising a polyether polymer that has a terminal silicone functional group, the condensation product of an aminoalkylalkoxysilane with an epoxy compound and an alkoxy silane and an organic titanic acid ester, and a condensation catalyst or a silanol compound. Product literature from Union Carbide entitled SILMOD.TM. Polyethers discloses curable adhesives comprising a silicon-modified polyethers and an epoxy resin with a 2:1 ratio for the best balance of properties. The above references disclose using adhesives in applications requiring hardness and strength such as for sealants and in building applications. These hard and strong adhesives are rigid. For example, the Silmod.TM. product literature teaches an adhesive with the best balance of properties having an elongation of 370 percent. None of the documents discuss using epoxy resin and a polymer that has silicone-containing, crosslinkable, terminal, functional group in a retroreflective article.